Method of protecting a well casing and tubing against leakage, collapse, and corrosion



United States Patent 3,912,606 METHOD GF PRQTECTING A WELL CAdlNG AND TUBING AGAHNST LEAKAGE, CGLLAPSE, AND CORROSION Jesse M. Brooke, Sweeny, Ten, assignor to Phillips Petroleum Company, a corporation of Deiaware No Drawing. Filed Get. 17, 1958, Ser. No. 767,759 6 Claims. (Cl. 166--1) This invention relates to a novel packer fluid to be employed in wells, particularly when producing oil or gas from said wells.

This application is a continuation-in-part application of my copending application Serial No. 658,252, filed May 10, 1957, now abandoned.

In drilling a well, it is often necessary to pack off the annulus between the producing tubing and the casing, for example, when producing the oil or gas from the well. This is accomplished by placing a packer in the annulus and leaving some type of fluid in the annulus above the packer. The purpose of this packer fluid is to eifect the pressure diiferential across the packer and the casing, thereby preventing leakage from the tubing or from the formation into the casing, and preventing collapse of the casing. High density drilling muds are commonly employed as packed fluids but these muds are often unsatisfactory due to solidification, settling of the suspended solids, etc. Consequently, the removal of the packer or production tubing is often very diflicult and necessarily entails expensive and timeconsuming workover operations. These high density drilling muds are unsatisfactory as packer fluid because of the high concentration of solids, such as drilled clay or shale solids, and mud reagents; they are also unsatsifactory because of the high amount of soluble contaminants, such as lime or calcium compounds. The solids in the high density muds tend to settle out and deposit above the packer. solidification of the high density mud can result by reaction, for example, of the dissolved solids in the liquid phase with the solid phase. Decomposition of organic matter often causes acid corrosion of the casing and tubing. Since it is expensive to replace the high density mud with a cleaner, high density mud, in order to circumvent these difliculties, it is generally not done.

Accordingly, an object of my invention is to provide a novel packer fluid.

Another object is to provide a novel packer fluid having a relatively high density.

A further object is to provide a packer fluid the components of which will not settle after standing.

A further object is to provide a novel packer fluid characterized by its non-corresiveness, the almost complete absence of inorganic suspended solids such as drilled clay solids, and its non-solidifying properties.

A further object is to provide an improved method of packing off the annulus between a casing and tubing suspended therein, in such a manner as to protect said casing and tubing against leakage, collapse, and corrosion.

Other objects and advantages of my invention will become apparent, to those skilled in the art, from the accompanying discussion and appended claims.

Accordingly, I propose to provide a novel packer fluid and an improved method of packing off the annulus between a casing and a tubing suspended therein. My novel packer fluid broadly comprises an aqueous solution of sodium nitrate. This packer fluid can further comprise, in addition to sodium nitrate, a salt selected from the group consisting of sodium chloride, potassium chloride, and sodium carbonate, and mixtures of these salts. Especially preferred packer fluids are aqueous solutions of sodium nitrate per se, sodium nitrate and potassium chloride, and sodium nitrate, potassium chloride and sodium carbonate. A packer fluid consisting of an aqueous solution of sodium nitrate and sodium chloride is also a preferred packer fluid, and in making up this packer fluid the water and sodium chloride can be employed in part or entirely in the form of sea water or field brine.

More particularly, the packer fluid comprises an aqueous neutral or alkaline solution of these water soluble salts, the packer fluid having a suflicient high density required by the depth of the well or the conditions prevailing in the well in which the packer fluid is employed. The salts employed are non-reactive, non-corrosive and generally soluble in hot or cold water. The packer fluid will not be affected by relatively high pressures or temperatures encountered in a well and will be able to stand in the well indefinitely without causing diificulties due to solidification, settling of solids, corrosion, etc.

In addition, minor amounts of other salts or compounds which are soluble or dispersible in water can be added, for example, to inhibit corrosion, such other components including conventionally known corrosion inhibitors such as mercaptobenzothiozole, arsenites, etc. In addition, reagents can be added to increase the viscosity of the packer fluid, for example, carboxymethyl cellulose and sodium silicate.

The amount of salt or salts in the packer fluids of this invention can vary over a Wide range, depending on the particular salts employed, the density desired, etc., but generally the total salt content will vary in the range of 10 to 56 weight percent. Where, in addition to sodium nitrate, other of the aforementioned salts are incorporated in the packer fluid, the dry weight ratio of sodium nitrate to that of the total of other salts will vary in the range of 1:1 to 55:1, preferably in the range of 3:1 to 10:1. For example, in an aqueous packer fluid comprising (a) sodium nitrate, (b) potassium chloride, and (0) sodium carbonate, the dry Weight ratio of (a) to (c) is about 9.4. The dry weight ratio of (b) to (c) of this latter-mentioned packer fluid is about 1.5.

The components employed in my packer fluid may serve the purpose of increasing the density of the packer fluid, inhibiting corrosion, rendering the solution neutral or alkaline, or a combination of these purposes. For example, sodium nitrate can be employed for the purpose of inhibiting corrosion as Well as for the purpose of in creasing the density of the packer fluid; potassium chloride can be employed for the purpose of merely increasing the density; and sodium carbonate can be employed for the purpose of maintaining the packer fluid neutral or alkaline, that is, maintaining a pH of 7 or greater.

The packer fluid can be prepared by adding the components to hot or cold water. Where saturated solutions are desired, an excess of the component or components can be added, and the undissolved portions can be allowed to settle out and be subsequently removed by decanting the solution. If desired, the water or the solution can be heated so as to increase the rate of solution and to increase the solubility of the various components; the hot solution can be pumped into the annulus of the well where thermal equilibrium can be attained.

The packer fluid can be placed in the well according to well known procedure. For example, after drilling is completed and the Well is conditioned by cleaning out the cuttings and circulating drilling mud, the drill stream is run out of the Well and the casing is run into the well and cemented. The production tubing and packer are then put into the Well. The packer fluid is introduced into the Well following a slug of clean water or other cleaning fluid if desired. The packer can be set by tuming the tubing or raising or lowering the same. The casing can be perforated either before or after the placing of the packer fluid. Surface equipment can then be 3 installed and the well completed because the packer fluid of this invention does not contain any solid components or other material which will settle out during standing; thepacker-will not be frozen in place even after pro? longed standing. Moreover, since the packer fluid of this invention is non-corrosive, no corrosion problems will be encountered.

EXAMPLE I A particularly useful packer fluid was prepared having a density of about 1.48 g./cc., equivalent to about 12.35 lbs./gal., the composition of which is set forth in the following table. The solution was saturated with respect to the salts at 78 F.

In order to determine the range of weight values of a comparatively high density salt solution, at various salt concentrations, the following procedure was carried out. A dry salt mixture was made up comprising 78.86 weight percent sodium nitrate, 12.75 weight percent potassium chloride, and 8.39 Weight percent sodium carbonate. Aqueous salt solutions were made at total salt concentrations from 10.0 to 56.2 weight percent. The salt solutions were stirred at room temperatureu ntil the salt mixture Went into solution. The Weights of the salt solutions at 70 F. were determined by a mud balance. Viscosity determinations of the salt solutions were made a Dial reading of meter at 600 rpm. divided by 2. b Dial reading of meter at 600 rpm. minus dial reading at 300 r.p.m.

EXAMPLE III A number of useful packer fluids of various concentrations and densities, consisting of aqueous solutions of sodium nitrate, are set forth in Table III.

Table III Component, Weight Percent Solution Density (lb/gal.)

H2O NaNO;

90 8.9 at 80 F., unsat 80 9.5 at 80 F., unsat 76 24 9.9 at 80 F., unset. 70 10.3 at 80 F., unsat 60 40 11.1 at 80 F., unsat 52 48 11.7 at 80 F., sat. 48 52 11.9 at 120 F., sat 44 56 12.2 at 165 F., sat

EXAMPLE IV Another series. of useful packer fluids, consisting of aqueous solutions of sodium nitrate and potassum chloride, having various concentrations and densities, are set forth in Table IV.

Table IV Component, Weight Solution Density (lb./gal.)

H2O NaNO; KCl

60 20 20 10.9 at F., sat. 60 35 5 10.9 at 8 F., unsat 50 45 5 11.9 at 80 F., unsat 46 44 10 12.2 at 80 F., sat 41 48 11 12.4 at F., set 39 '52 9 e 12.7 at 165 F., sat 44 55 1 12.2 at 165 F., sat

The density of the packer fluid to be employed in any particular instance will, of course, also depend upon such considerations as the depth of the well and the pressure in the well where the packer fluid is employed. Generally the density of the packer fluid will be greater than about 9 lbs./ gal. and the term high density as employed herein and in the appended claims is to be understood as being a density of at least about 9 lbs./ gal. The packer fluids of my invention having a density in the range between about 9 and 13 lbs./ gal. will be satisfactory in the great majority of wells being drilled and produced at the present time.

Various modifications and alterations of my invention will become apparent, to those skilled in the art, from the foregoing discussion, and it is to be understood that my invention is not to be unduly limited thereto.

I claim:

1. A method which comprises packing off the annulus between a casing and a tubing in a well, and filling said annulus with packer fluid consisting essentially of a solidsfree aqueous solution of sodium nitrate, said solution having a density of at least 9 pounds per gallon.

2. A method of protecting a casing and a tubing in a well against leakage, collapse, and corrosion, which method comprises packing off the annulus between said casing and tubing, and filling said annulus with a packer fluid consisting essentially of a solids-free aqueous solution of sodium nitrate, said solution having a density in the range of about 9 to about 13 pounds per gallon.

3.' A method of protecting a casing and a tubing in a well against leakage, collapse, and corrosion, which method comprises packing oil the annulus between said casing and tubing, and filling said annulus with a packer fluid consisting essentially of a solids-free aqueous solution of sodium nitrate, and a salt selected from the group consisting of sodium chloride, potassium chloride, sodium carbonate, and mixtures thereof, said solution having a density in the range of about 9 to about 13 pounds per gallon, wherein the dry weight ratio of said sodium nitrate to that of the total of the other salts is in the range of 1:110 55:1.

4. A method of protecting a casing and a tubing in a well against leakage, collapse, and corrosion, which method comprises packing off the annulus between said casing and tubing, and filling said annulus with a packer fluid consisting essentially of a solids-free aqueous solution of sodium nitrate, and sodium chloride, said solution having a total salt concentration in the range of 10 to 56 weight percent and a density in the range of about 9 to about 13 pounds per gallon, wherein the dry weight ratio of said sodium nitrate to that of the total of other salts is in the range of 1:1 to 55:1.

5. Arnethod of protectinga casing and a tubing in well against leakage, collapse, and corrosion, which method comprises packing off the annulus between said cas ing and tubing, and filling said annulus with a packer fluid consisting essentially of a solids-free aqueous solut-ion of sodium nitrate, and potassium chloride and sodium chloride, said solution having a total salt concentration in the range of 10 to 56 weight percent and a density in the range of about 9 to about 13 pounds per gallon, wherein the dry weight ratio of said sodium nitrate to that of the total of other salt is in the range of 1:1 to 55:1.

6. A method of protecting a casing and a tubing in a well against leakage, collapse, and corrosion, which method comprises packing oil? the annulus between said casing and tubing, and filling said annulus with a packer fluid consisting essentially of a solids-free aqueous solution of sodium nitrate, potassium chloride, and sodium carbonate, said solution having a density in the range of about 9 to about 13 pound per gallon, wherein the dry weight ratio of said sodium nitrate to that of the total of other salts is in the range of 1:1 to 55:1.

References Cited in the file of this patent UNITED STATES PATENTS 2,073,413 Cross et al. Mar. 9, 1937 2,239,647 Garrison Apr. 22, 1941 2,793,996 Lummus May 28, 1957 2,805,722 Morgan et al. Sept. 10, 1957 2,898,294 Priest et al. Aug. 4, 1959 

1. A METHOD WHICH COMPRISES PACKING OFF THE ANNULUS BETWEEN A CASING AND A TUBING IN A WELL, AND FILLING SAID ANNULUS WITH PACKER FLUID CONSISTING ESSENTIALLY OF A SOLIDSFREE AQUEOUS SOLUTION OF SODIUM NITRATE, SAID SOLUTION HAVING A DENSITY OF AT LEAST 9 POUNDS PER GALLON. 